There are a few oddities with controllers.
I have tested a few and interestingly, as long as it was some sort of "360"-style pad *and had a cable*, it worked right away.
Everything else was borderline problematic, as soon as it was wireless. Even with windows drivers, they sometimes just would not work with browser based stuff.
That said.. while testing you always have to remember that a user interaction is required to fire up the controller in the browser. On start of layout it won't be visible, for security reasons (so that a malicious website cannot identify users by their various controller setups). Only after the first button has been pressed they show up.